This invention relates to scrap recovery. More particularly, this invention relates to a method of operating a scrap treating furnace for the separation and recovery of metallic components of metallic scrap having different incipient melting temperatures.
Recycling of materials, such as steel or aluminum used in the packaging and automotive industries, has become increasingly important as energy and material costs continue to rise. However, in such fields, it has become the practice to use more than one type of metal or metal alloy in the device, e.g. an aluminum lid in a beverage can and a steel body or an aluminum can body comprising a different alloy than the lid.
This usage of different metallic components in a container or the like has economically hampered the recycling of such devices. For example, attempts to recycle a beverage can having a body fabricated from one aluminum alloy and a top or lid constructed from a different aluminum alloy may result in a melt having the composition of neither alloy.
The reuse of such recovered aluminum may then necessitate purification, realloying or costly dilution with pure aluminum or other alloying constituents to arrive at a useful ratio of alloy constituents, i.e., a particular alloy useful in a given application. This greatly reduces the value of the melted recycled metal since it cannot be reused, for example, as a can body or can lid without major dilutions, purifications, realloying or other modification.
The problem of segregation of different alloys is recognized in U.S. Pat. No. 3,736,896, where there is disclosed the separating of aluminum alloy tops or lids from steel bodied cans by melting a small band of aluminum around the periphery of the can body to provide a separating area allowing separation of the aluminum end from the steel cylindrical body. In this disclosure, induction heating is used to melt the band wherein an encircling inductor surrounds a bead and is connected to a high frequency power supply. However, this approach seems to presume that used beverage can are not usually crushed and the ends remain perfectly circular. Further, to melt the ends off in this manner would not seem to be economical since the ends would have to be removed individually.
In U.S. Pat. No. 4,016,003, containers having aluminum alloy bodies and lids are shredded to particles in the range of 1 to 11/2 inch and then subjected to temperatures of around 700.degree. F. to remove paints and lacquers. In addition, U.S. Pat. No. 4,269,632 indicates that since the conventional alloys for can ends, e.g., Aluminum Association (AA) alloy 5182, 5082 or 5052, and for can bodies, e.g., AA 3004 or 3003, differ significantly in composition, and in the manufactured can, the end and body are essentially inseparable and that an economical recycle system requires the use of the entire can. U.S. Pat. No. 4,269,632 further notes that the recycling of cans results in a melt composition which differs significantly from the compositions of both the conventional can end and can body alloys. In this patent, it is suggested that both can end and body be fabricated from the same alloy to obviate the recycling problem. With respect to can ends and bodies made from AA 5182 and 3004 it is indicated that normally pure aluminum must be added regardless of the alloy prepared.
Recyclable scrap metal also may contain decorative or protective coatings thereon which may contain elements, such as titanium. Titanium, in high levels, is not normally desirable in many alloys, such as alloys used in the manufacture of aluminum beverage can bodies or lids. It is, therefore, desirable to remove such coatings prior to melting of the recyclable scrap to avoid the dilution, purification and realloying problems previously mentioned.
The coatings may be removed by a solvent delacquering step or they may be removed by thermal treatment. One such thermal treatment comprises feeding the scrap into a rotary kiln or furnace which passes hot flue gases therethrough to heat the scrap to a temperature of about 538.degree. C. (1000.degree. F.) while agitating the scrap to provide uniform heating and maximum heat transfer. Apparatus specifically designed for this purpose is manufactured by APROS (Automated Production Systems Corporation) comprising a rotary kiln heated by flue gases from a combustion chamber.
Conventionally, scrap, such as aluminum scrap, after such removal of coatings, is melted without any attempt to segregate the scrap by various alloys of a given metal, e.g., without attempting to segregate aluminum can lids from can bodies.
It would be advantageous to have a method whereby scrap could be easily segregated or divided into components by alloy type. In this manner, each component could be separately melted and refabricated in accordance with normal procedures without, inter alia, expensive dilutions or purification steps.